FreeBSD/Linux Kernel Cross Reference
sys/kern/sched_ule.c

     /*-
      * Copyright (c) 2002-2007, Jeffrey Roberson <jeff@freebsd.org>
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
      *    notice unmodified, this list of conditions, and the following
     *    disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
     * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     */
    
    /*
     * This file implements the ULE scheduler.  ULE supports independent CPU
     * run queues and fine grain locking.  It has superior interactive
     * performance under load even on uni-processor systems.
     *
     * etymology:
     *   ULE is the last three letters in schedule.  It owes its name to a
     * generic user created for a scheduling system by Paul Mikesell at
     * Isilon Systems and a general lack of creativity on the part of the author.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/7.4/sys/kern/sched_ule.c 213722 2010-10-12 15:26:37Z jhb $");
    
    #include "opt_hwpmc_hooks.h"
    #include "opt_kdtrace.h"
    #include "opt_sched.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kdb.h>
    #include <sys/kernel.h>
    #include <sys/ktr.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/proc.h>
    #include <sys/resource.h>
    #include <sys/resourcevar.h>
    #include <sys/sched.h>
    #include <sys/smp.h>
    #include <sys/sx.h>
    #include <sys/sysctl.h>
    #include <sys/sysproto.h>
    #include <sys/turnstile.h>
    #include <sys/umtx.h>
    #include <sys/vmmeter.h>
    #include <sys/cpuset.h>
    #ifdef KTRACE
    #include <sys/uio.h>
    #include <sys/ktrace.h>
    #endif
    
    #ifdef HWPMC_HOOKS
    #include <sys/pmckern.h>
    #endif
    
    #ifdef KDTRACE_HOOKS
    #include <sys/dtrace_bsd.h>
    int                             dtrace_vtime_active;
    dtrace_vtime_switch_func_t      dtrace_vtime_switch_func;
    #endif
    
    #include <machine/cpu.h>
    #include <machine/smp.h>
    
    #if !defined(__i386__) && !defined(__amd64__) && !defined(__arm__)
    #error "This architecture is not currently compatible with ULE"
    #endif
    
    #define KTR_ULE 0
    
    /*
     * Thread scheduler specific section.  All fields are protected
     * by the thread lock.
     */
    struct td_sched {       
            TAILQ_ENTRY(td_sched) ts_procq; /* Run queue. */
            struct thread   *ts_thread;     /* Active associated thread. */
            struct runq     *ts_runq;       /* Run-queue we're queued on. */
            short           ts_flags;       /* TSF_* flags. */
            u_char          ts_rqindex;     /* Run queue index. */
            u_char          ts_cpu;         /* CPU that we have affinity for. */
            int             ts_slice;       /* Ticks of slice remaining. */
           u_int           ts_slptime;     /* Number of ticks we vol. slept */
           u_int           ts_runtime;     /* Number of ticks we were running */
           /* The following variables are only used for pctcpu calculation */
           int             ts_ltick;       /* Last tick that we were running on */
           int             ts_incrtick;    /* Last tick that we incremented on */
           int             ts_ftick;       /* First tick that we were running on */
           int             ts_ticks;       /* Tick count */
   #ifdef SMP
           int             ts_rltick;      /* Real last tick, for affinity. */
   #endif
   };
   /* flags kept in ts_flags */
   #define TSF_BOUND       0x0001          /* Thread can not migrate. */
   #define TSF_XFERABLE    0x0002          /* Thread was added as transferable. */
   
   static struct td_sched td_sched0;
   
   #define THREAD_CAN_MIGRATE(td)  ((td)->td_pinned == 0)
   #define THREAD_CAN_SCHED(td, cpu)       \
       CPU_ISSET((cpu), &(td)->td_cpuset->cs_mask)
   
   /*
    * Cpu percentage computation macros and defines.
    *
    * SCHED_TICK_SECS:     Number of seconds to average the cpu usage across.
    * SCHED_TICK_TARG:     Number of hz ticks to average the cpu usage across.
    * SCHED_TICK_MAX:      Maximum number of ticks before scaling back.
    * SCHED_TICK_SHIFT:    Shift factor to avoid rounding away results.
    * SCHED_TICK_HZ:       Compute the number of hz ticks for a given ticks count.
    * SCHED_TICK_TOTAL:    Gives the amount of time we've been recording ticks.
    */
   #define SCHED_TICK_SECS         10
   #define SCHED_TICK_TARG         (hz * SCHED_TICK_SECS)
   #define SCHED_TICK_MAX          (SCHED_TICK_TARG + hz)
   #define SCHED_TICK_SHIFT        10
   #define SCHED_TICK_HZ(ts)       ((ts)->ts_ticks >> SCHED_TICK_SHIFT)
   #define SCHED_TICK_TOTAL(ts)    (max((ts)->ts_ltick - (ts)->ts_ftick, hz))
   
   /*
    * These macros determine priorities for non-interactive threads.  They are
    * assigned a priority based on their recent cpu utilization as expressed
    * by the ratio of ticks to the tick total.  NHALF priorities at the start
    * and end of the MIN to MAX timeshare range are only reachable with negative
    * or positive nice respectively.
    *
    * PRI_RANGE:   Priority range for utilization dependent priorities.
    * PRI_NRESV:   Number of nice values.
    * PRI_TICKS:   Compute a priority in PRI_RANGE from the ticks count and total.
    * PRI_NICE:    Determines the part of the priority inherited from nice.
    */
   #define SCHED_PRI_NRESV         (PRIO_MAX - PRIO_MIN)
   #define SCHED_PRI_NHALF         (SCHED_PRI_NRESV / 2)
   #define SCHED_PRI_MIN           (PRI_MIN_TIMESHARE + SCHED_PRI_NHALF)
   #define SCHED_PRI_MAX           (PRI_MAX_TIMESHARE - SCHED_PRI_NHALF)
   #define SCHED_PRI_RANGE         (SCHED_PRI_MAX - SCHED_PRI_MIN)
   #define SCHED_PRI_TICKS(ts)                                             \
       (SCHED_TICK_HZ((ts)) /                                              \
       (roundup(SCHED_TICK_TOTAL((ts)), SCHED_PRI_RANGE) / SCHED_PRI_RANGE))
   #define SCHED_PRI_NICE(nice)    (nice)
   
   /*
    * These determine the interactivity of a process.  Interactivity differs from
    * cpu utilization in that it expresses the voluntary time slept vs time ran
    * while cpu utilization includes all time not running.  This more accurately
    * models the intent of the thread.
    *
    * SLP_RUN_MAX: Maximum amount of sleep time + run time we'll accumulate
    *              before throttling back.
    * SLP_RUN_FORK:        Maximum slp+run time to inherit at fork time.
    * INTERACT_MAX:        Maximum interactivity value.  Smaller is better.
    * INTERACT_THRESH:     Threshhold for placement on the current runq.
    */
   #define SCHED_SLP_RUN_MAX       ((hz * 5) << SCHED_TICK_SHIFT)
   #define SCHED_SLP_RUN_FORK      ((hz / 2) << SCHED_TICK_SHIFT)
   #define SCHED_INTERACT_MAX      (100)
   #define SCHED_INTERACT_HALF     (SCHED_INTERACT_MAX / 2)
   #define SCHED_INTERACT_THRESH   (30)
   
   /*
    * tickincr:            Converts a stathz tick into a hz domain scaled by
    *                      the shift factor.  Without the shift the error rate
    *                      due to rounding would be unacceptably high.
    * realstathz:          stathz is sometimes 0 and run off of hz.
    * sched_slice:         Runtime of each thread before rescheduling.
    * preempt_thresh:      Priority threshold for preemption and remote IPIs.
    */
   static int sched_interact = SCHED_INTERACT_THRESH;
   static int realstathz;
   static int tickincr;
   static int sched_slice;
   #ifdef PREEMPTION
   #ifdef FULL_PREEMPTION
   static int preempt_thresh = PRI_MAX_IDLE;
   #else
   static int preempt_thresh = PRI_MIN_KERN;
   #endif
   #else 
   static int preempt_thresh = 0;
   #endif
   
   /*
    * tdq - per processor runqs and statistics.  All fields are protected by the
    * tdq_lock.  The load and lowpri may be accessed without to avoid excess
    * locking in sched_pickcpu();
    */
   struct tdq {
           struct mtx      *tdq_lock;              /* Pointer to group lock. */
           struct runq     tdq_realtime;           /* real-time run queue. */
           struct runq     tdq_timeshare;          /* timeshare run queue. */
           struct runq     tdq_idle;               /* Queue of IDLE threads. */
           int             tdq_load;               /* Aggregate load. */
           u_char          tdq_idx;                /* Current insert index. */
           u_char          tdq_ridx;               /* Current removal index. */
   #ifdef SMP
           u_char          tdq_lowpri;             /* Lowest priority thread. */
           int             tdq_transferable;       /* Transferable thread count. */
           LIST_ENTRY(tdq) tdq_siblings;           /* Next in tdq group. */
           struct tdq_group *tdq_group;            /* Our processor group. */
   #else
           int             tdq_sysload;            /* For loadavg, !ITHD load. */
   #endif
   } __aligned(64);
   
   
   #ifdef SMP
   /*
    * tdq groups are groups of processors which can cheaply share threads.  When
    * one processor in the group goes idle it will check the runqs of the other
    * processors in its group prior to halting and waiting for an interrupt.
    * These groups are suitable for SMT (Symetric Multi-Threading) and not NUMA.
    * In a numa environment we'd want an idle bitmap per group and a two tiered
    * load balancer.
    */
   struct tdq_group {
           struct mtx      tdg_lock;       /* Protects all fields below. */
           int             tdg_cpus;       /* Count of CPUs in this tdq group. */
           cpumask_t       tdg_cpumask;    /* Mask of cpus in this group. */
           cpumask_t       tdg_idlemask;   /* Idle cpus in this group. */
           cpumask_t       tdg_mask;       /* Bit mask for first cpu. */
           int             tdg_load;       /* Total load of this group. */
           int     tdg_transferable;       /* Transferable load of this group. */
           LIST_HEAD(, tdq) tdg_members;   /* Linked list of all members. */
           char            tdg_name[16];   /* lock name. */
   } __aligned(64);
   
   #define SCHED_AFFINITY_DEFAULT  (max(1, hz / 300))
   #define SCHED_AFFINITY(ts)      ((ts)->ts_rltick > ticks - affinity)
   
   /*
    * Run-time tunables.
    */
   static int rebalance = 1;
   static int balance_interval = 128;      /* Default set in sched_initticks(). */
   static int pick_pri = 1;
   static int affinity;
   static int tryself = 1;
   static int steal_htt = 1;
   static int steal_idle = 1;
   static int steal_thresh = 2;
   static int topology = 0;
   
   /*
    * One thread queue per processor.
    */
   static volatile cpumask_t tdq_idle;
   static int tdg_maxid;
   static struct tdq       tdq_cpu[MAXCPU];
   static struct tdq_group tdq_groups[MAXCPU];
   static struct tdq       *balance_tdq;
   static int balance_group_ticks;
   static int balance_ticks;
   
   #define TDQ_SELF()      (&tdq_cpu[PCPU_GET(cpuid)])
   #define TDQ_CPU(x)      (&tdq_cpu[(x)])
   #define TDQ_ID(x)       ((int)((x) - tdq_cpu))
   #define TDQ_GROUP(x)    (&tdq_groups[(x)])
   #define TDG_ID(x)       ((int)((x) - tdq_groups))
   #else   /* !SMP */
   static struct tdq       tdq_cpu;
   static struct mtx       tdq_lock;
   
   #define TDQ_ID(x)       (0)
   #define TDQ_SELF()      (&tdq_cpu)
   #define TDQ_CPU(x)      (&tdq_cpu)
   #endif
   
   #define TDQ_LOCK_ASSERT(t, type)        mtx_assert(TDQ_LOCKPTR((t)), (type))
   #define TDQ_LOCK(t)             mtx_lock_spin(TDQ_LOCKPTR((t)))
   #define TDQ_LOCK_FLAGS(t, f)    mtx_lock_spin_flags(TDQ_LOCKPTR((t)), (f))
   #define TDQ_UNLOCK(t)           mtx_unlock_spin(TDQ_LOCKPTR((t)))
   #define TDQ_LOCKPTR(t)          ((t)->tdq_lock)
   
   static void sched_priority(struct thread *);
   static void sched_thread_priority(struct thread *, u_char);
   static int sched_interact_score(struct thread *);
   static void sched_interact_update(struct thread *);
   static void sched_interact_fork(struct thread *);
   static void sched_pctcpu_update(struct td_sched *);
   
   /* Operations on per processor queues */
   static struct td_sched * tdq_choose(struct tdq *);
   static void tdq_setup(struct tdq *);
   static void tdq_load_add(struct tdq *, struct td_sched *);
   static void tdq_load_rem(struct tdq *, struct td_sched *);
   static __inline void tdq_runq_add(struct tdq *, struct td_sched *, int);
   static __inline void tdq_runq_rem(struct tdq *, struct td_sched *);
   void tdq_print(int cpu);
   static void runq_print(struct runq *rq);
   static void tdq_add(struct tdq *, struct thread *, int);
   #ifdef SMP
   static void tdq_move(struct tdq *, struct tdq *);
   static int tdq_idled(struct tdq *);
   static void tdq_notify(struct td_sched *);
   static struct td_sched *tdq_steal(struct tdq *, int);
   static struct td_sched *runq_steal(struct runq *, int);
   static int sched_pickcpu(struct thread *, int);
   static void sched_balance(void);
   static void sched_balance_groups(void);
   static void sched_balance_group(struct tdq_group *);
   static void sched_balance_pair(struct tdq *, struct tdq *);
   static inline struct tdq *sched_setcpu(struct td_sched *, int, int);
   static inline void thread_unblock_switch(struct thread *, struct mtx *);
   static struct mtx *sched_switch_migrate(struct tdq *, struct thread *, int);
   #endif
   
   static void sched_setup(void *dummy);
   SYSINIT(sched_setup, SI_SUB_RUN_QUEUE, SI_ORDER_FIRST, sched_setup, NULL);
   
   static void sched_initticks(void *dummy);
   SYSINIT(sched_initticks, SI_SUB_CLOCKS, SI_ORDER_THIRD, sched_initticks,
       NULL);
   
   /*
    * Print the threads waiting on a run-queue.
    */
   static void
   runq_print(struct runq *rq)
   {
           struct rqhead *rqh;
           struct td_sched *ts;
           int pri;
           int j;
           int i;
   
           for (i = 0; i < RQB_LEN; i++) {
                   printf("\t\trunq bits %d 0x%zx\n",
                       i, rq->rq_status.rqb_bits[i]);
                   for (j = 0; j < RQB_BPW; j++)
                           if (rq->rq_status.rqb_bits[i] & (1ul << j)) {
                                   pri = j + (i << RQB_L2BPW);
                                   rqh = &rq->rq_queues[pri];
                                   TAILQ_FOREACH(ts, rqh, ts_procq) {
                                           printf("\t\t\ttd %p(%s) priority %d rqindex %d pri %d\n",
                                               ts->ts_thread, ts->ts_thread->td_proc->p_comm, ts->ts_thread->td_priority, ts->ts_rqindex, pri);
                                   }
                           }
           }
   }
   
   /*
    * Print the status of a per-cpu thread queue.  Should be a ddb show cmd.
    */
   void
   tdq_print(int cpu)
   {
           struct tdq *tdq;
   
           tdq = TDQ_CPU(cpu);
   
           printf("tdq %d:\n", TDQ_ID(tdq));
           printf("\tlockptr         %p\n", TDQ_LOCKPTR(tdq));
           printf("\tload:           %d\n", tdq->tdq_load);
           printf("\ttimeshare idx:  %d\n", tdq->tdq_idx);
           printf("\ttimeshare ridx: %d\n", tdq->tdq_ridx);
           printf("\trealtime runq:\n");
           runq_print(&tdq->tdq_realtime);
           printf("\ttimeshare runq:\n");
           runq_print(&tdq->tdq_timeshare);
           printf("\tidle runq:\n");
           runq_print(&tdq->tdq_idle);
   #ifdef SMP
           printf("\tload transferable: %d\n", tdq->tdq_transferable);
           printf("\tlowest priority:   %d\n", tdq->tdq_lowpri);
           printf("\tgroup:             %d\n", TDG_ID(tdq->tdq_group));
           printf("\tLock name:         %s\n", tdq->tdq_group->tdg_name);
   #endif
   }
   
   #define TS_RQ_PPQ       (((PRI_MAX_TIMESHARE - PRI_MIN_TIMESHARE) + 1) / RQ_NQS)
   /*
    * Add a thread to the actual run-queue.  Keeps transferable counts up to
    * date with what is actually on the run-queue.  Selects the correct
    * queue position for timeshare threads.
    */
   static __inline void
   tdq_runq_add(struct tdq *tdq, struct td_sched *ts, int flags)
   {
           TDQ_LOCK_ASSERT(tdq, MA_OWNED);
           THREAD_LOCK_ASSERT(ts->ts_thread, MA_OWNED);
   #ifdef SMP
           if (THREAD_CAN_MIGRATE(ts->ts_thread)) {
                   tdq->tdq_transferable++;
                   tdq->tdq_group->tdg_transferable++;
                   ts->ts_flags |= TSF_XFERABLE;
           }
   #endif
           if (ts->ts_runq == &tdq->tdq_timeshare) {
                   u_char pri;
   
                   pri = ts->ts_thread->td_priority;
                   KASSERT(pri <= PRI_MAX_TIMESHARE && pri >= PRI_MIN_TIMESHARE,
                           ("Invalid priority %d on timeshare runq", pri));
                   /*
                    * This queue contains only priorities between MIN and MAX
                    * realtime.  Use the whole queue to represent these values.
                    */
                   if ((flags & (SRQ_BORROWING|SRQ_PREEMPTED)) == 0) {
                           pri = (pri - PRI_MIN_TIMESHARE) / TS_RQ_PPQ;
                           pri = (pri + tdq->tdq_idx) % RQ_NQS;
                           /*
                            * This effectively shortens the queue by one so we
                            * can have a one slot difference between idx and
                            * ridx while we wait for threads to drain.
                            */
                           if (tdq->tdq_ridx != tdq->tdq_idx &&
                               pri == tdq->tdq_ridx)
                                   pri = (unsigned char)(pri - 1) % RQ_NQS;
                   } else
                           pri = tdq->tdq_ridx;
                   runq_add_pri(ts->ts_runq, ts, pri, flags);
           } else
                   runq_add(ts->ts_runq, ts, flags);
   }
   
   /* 
    * Remove a thread from a run-queue.  This typically happens when a thread
    * is selected to run.  Running threads are not on the queue and the
    * transferable count does not reflect them.
    */
   static __inline void
   tdq_runq_rem(struct tdq *tdq, struct td_sched *ts)
   {
           TDQ_LOCK_ASSERT(tdq, MA_OWNED);
           KASSERT(ts->ts_runq != NULL,
               ("tdq_runq_remove: thread %p null ts_runq", ts->ts_thread));
   #ifdef SMP
           if (ts->ts_flags & TSF_XFERABLE) {
                   tdq->tdq_transferable--;
                   tdq->tdq_group->tdg_transferable--;
                   ts->ts_flags &= ~TSF_XFERABLE;
           }
   #endif
           if (ts->ts_runq == &tdq->tdq_timeshare) {
                   if (tdq->tdq_idx != tdq->tdq_ridx)
                           runq_remove_idx(ts->ts_runq, ts, &tdq->tdq_ridx);
                   else
                           runq_remove_idx(ts->ts_runq, ts, NULL);
                   /*
                    * For timeshare threads we update the priority here so
                    * the priority reflects the time we've been sleeping.
                    */
                   ts->ts_ltick = ticks;
                   sched_pctcpu_update(ts);
                   sched_priority(ts->ts_thread);
           } else
                   runq_remove(ts->ts_runq, ts);
   }
   
   /*
    * Load is maintained for all threads RUNNING and ON_RUNQ.  Add the load
    * for this thread to the referenced thread queue.
    */
   static void
   tdq_load_add(struct tdq *tdq, struct td_sched *ts)
   {
           int class;
   
           TDQ_LOCK_ASSERT(tdq, MA_OWNED);
           THREAD_LOCK_ASSERT(ts->ts_thread, MA_OWNED);
           class = PRI_BASE(ts->ts_thread->td_pri_class);
           tdq->tdq_load++;
           CTR2(KTR_SCHED, "cpu %d load: %d", TDQ_ID(tdq), tdq->tdq_load);
           if (class != PRI_ITHD &&
               (ts->ts_thread->td_proc->p_flag & P_NOLOAD) == 0)
   #ifdef SMP
                   tdq->tdq_group->tdg_load++;
   #else
                   tdq->tdq_sysload++;
   #endif
   }
   
   /*
    * Remove the load from a thread that is transitioning to a sleep state or
    * exiting.
    */
   static void
   tdq_load_rem(struct tdq *tdq, struct td_sched *ts)
   {
           int class;
   
           THREAD_LOCK_ASSERT(ts->ts_thread, MA_OWNED);
           TDQ_LOCK_ASSERT(tdq, MA_OWNED);
           class = PRI_BASE(ts->ts_thread->td_pri_class);
           if (class != PRI_ITHD &&
               (ts->ts_thread->td_proc->p_flag & P_NOLOAD) == 0)
   #ifdef SMP
                   tdq->tdq_group->tdg_load--;
   #else
                   tdq->tdq_sysload--;
   #endif
           KASSERT(tdq->tdq_load != 0,
               ("tdq_load_rem: Removing with 0 load on queue %d", TDQ_ID(tdq)));
           tdq->tdq_load--;
           CTR1(KTR_SCHED, "load: %d", tdq->tdq_load);
           ts->ts_runq = NULL;
   }
   
   #ifdef SMP
   /*
    * sched_balance is a simple CPU load balancing algorithm.  It operates by
    * finding the least loaded and most loaded cpu and equalizing their load
    * by migrating some processes.
    *
    * Dealing only with two CPUs at a time has two advantages.  Firstly, most
    * installations will only have 2 cpus.  Secondly, load balancing too much at
    * once can have an unpleasant effect on the system.  The scheduler rarely has
    * enough information to make perfect decisions.  So this algorithm chooses
    * simplicity and more gradual effects on load in larger systems.
    *
    */
   static void
   sched_balance()
   {
           struct tdq_group *high;
           struct tdq_group *low;
           struct tdq_group *tdg;
           struct tdq *tdq;
           int cnt;
           int i;
   
           /*
            * Select a random time between .5 * balance_interval and
            * 1.5 * balance_interval.
            */
           balance_ticks = max(balance_interval / 2, 1);
           balance_ticks += random() % balance_interval;
           if (smp_started == 0 || rebalance == 0)
                   return;
           tdq = TDQ_SELF();
           TDQ_UNLOCK(tdq);
           low = high = NULL;
           i = random() % (tdg_maxid + 1);
           for (cnt = 0; cnt <= tdg_maxid; cnt++) {
                   tdg = TDQ_GROUP(i);
                   /*
                    * Find the CPU with the highest load that has some
                    * threads to transfer.
                    */
                   if ((high == NULL || tdg->tdg_load > high->tdg_load)
                       && tdg->tdg_transferable)
                           high = tdg;
                   if (low == NULL || tdg->tdg_load < low->tdg_load)
                           low = tdg;
                   if (++i > tdg_maxid)
                           i = 0;
           }
           if (low != NULL && high != NULL && high != low)
                   sched_balance_pair(LIST_FIRST(&high->tdg_members),
                       LIST_FIRST(&low->tdg_members));
           TDQ_LOCK(tdq);
   }
   
   /*
    * Balance load between CPUs in a group.  Will only migrate within the group.
    */
   static void
   sched_balance_groups()
   {
           struct tdq *tdq;
           int i;
   
           /*
            * Select a random time between .5 * balance_interval and
            * 1.5 * balance_interval.
            */
           balance_group_ticks = max(balance_interval / 2, 1);
           balance_group_ticks += random() % balance_interval;
           if (smp_started == 0 || rebalance == 0)
                   return;
           tdq = TDQ_SELF();
           TDQ_UNLOCK(tdq);
           for (i = 0; i <= tdg_maxid; i++)
                   sched_balance_group(TDQ_GROUP(i));
           TDQ_LOCK(tdq);
   }
   
   /*
    * Finds the greatest imbalance between two tdqs in a group.
    */
   static void
   sched_balance_group(struct tdq_group *tdg)
   {
           struct tdq *tdq;
           struct tdq *high;
           struct tdq *low;
           int load;
   
           if (tdg->tdg_transferable == 0)
                   return;
           low = NULL;
           high = NULL;
           LIST_FOREACH(tdq, &tdg->tdg_members, tdq_siblings) {
                   load = tdq->tdq_load;
                   if (high == NULL || load > high->tdq_load)
                           high = tdq;
                   if (low == NULL || load < low->tdq_load)
                           low = tdq;
           }
           if (high != NULL && low != NULL && high != low)
                   sched_balance_pair(high, low);
   }
   
   /*
    * Lock two thread queues using their address to maintain lock order.
    */
   static void
   tdq_lock_pair(struct tdq *one, struct tdq *two)
   {
           if (one < two) {
                   TDQ_LOCK(one);
                   TDQ_LOCK_FLAGS(two, MTX_DUPOK);
           } else {
                   TDQ_LOCK(two);
                   TDQ_LOCK_FLAGS(one, MTX_DUPOK);
           }
   }
   
   /*
    * Unlock two thread queues.  Order is not important here.
    */
   static void
   tdq_unlock_pair(struct tdq *one, struct tdq *two)
   {
           TDQ_UNLOCK(one);
           TDQ_UNLOCK(two);
   }
   
   /*
    * Transfer load between two imbalanced thread queues.
    */
   static void
   sched_balance_pair(struct tdq *high, struct tdq *low)
   {
           int transferable;
           int high_load;
           int low_load;
           int move;
           int diff;
           int i;
   
           tdq_lock_pair(high, low);
           /*
            * If we're transfering within a group we have to use this specific
            * tdq's transferable count, otherwise we can steal from other members
            * of the group.
            */
           if (high->tdq_group == low->tdq_group) {
                   transferable = high->tdq_transferable;
                   high_load = high->tdq_load;
                   low_load = low->tdq_load;
           } else {
                   transferable = high->tdq_group->tdg_transferable;
                   high_load = high->tdq_group->tdg_load;
                   low_load = low->tdq_group->tdg_load;
           }
           /*
            * Determine what the imbalance is and then adjust that to how many
            * threads we actually have to give up (transferable).
            */
           if (transferable != 0) {
                   diff = high_load - low_load;
                   move = diff / 2;
                   if (diff & 0x1)
                           move++;
                   move = min(move, transferable);
                   for (i = 0; i < move; i++)
                           tdq_move(high, low);
                   /*
                    * IPI the target cpu to force it to reschedule with the new
                    * workload.
                    */
                   ipi_selected(1 << TDQ_ID(low), IPI_PREEMPT);
           }
           tdq_unlock_pair(high, low);
           return;
   }
   
   /*
    * Move a thread from one thread queue to another.
    */
   static void
   tdq_move(struct tdq *from, struct tdq *to)
   {
           struct td_sched *ts;
           struct thread *td;
           struct tdq *tdq;
           int cpu;
   
           TDQ_LOCK_ASSERT(from, MA_OWNED);
           TDQ_LOCK_ASSERT(to, MA_OWNED);
   
           tdq = from;
           cpu = TDQ_ID(to);
           ts = tdq_steal(tdq, cpu);
           if (ts == NULL) {
                   struct tdq_group *tdg;
   
                   tdg = tdq->tdq_group;
                   LIST_FOREACH(tdq, &tdg->tdg_members, tdq_siblings) {
                           if (tdq == from || tdq->tdq_transferable == 0)
                                   continue;
                           ts = tdq_steal(tdq, cpu);
                           break;
                   }
                   if (ts == NULL)
                           return;
           }
           if (tdq == to)
                   return;
           td = ts->ts_thread;
           /*
            * Although the run queue is locked the thread may be blocked.  Lock
            * it to clear this and acquire the run-queue lock.
            */
           thread_lock(td);
           /* Drop recursive lock on from acquired via thread_lock(). */
           TDQ_UNLOCK(from);
           sched_rem(td);
           ts->ts_cpu = cpu;
           td->td_lock = TDQ_LOCKPTR(to);
           tdq_add(to, td, SRQ_YIELDING);
   }
   
   /*
    * This tdq has idled.  Try to steal a thread from another cpu and switch
    * to it.
    */
   static int
   tdq_idled(struct tdq *tdq)
   {
           struct tdq_group *tdg;
           struct tdq *steal;
           int highload;
           int highcpu;
           int cpu;
   
           if (smp_started == 0 || steal_idle == 0)
                   return (1);
           /* We don't want to be preempted while we're iterating over tdqs */
           spinlock_enter();
           tdg = tdq->tdq_group;
           /*
            * If we're in a cpu group, try and steal threads from another cpu in
            * the group before idling.  In a HTT group all cpus share the same
            * run-queue lock, however, we still need a recursive lock to
            * call tdq_move().
            */
           if (steal_htt && tdg->tdg_cpus > 1 && tdg->tdg_transferable) {
                   TDQ_LOCK(tdq);
                   LIST_FOREACH(steal, &tdg->tdg_members, tdq_siblings) {
                           if (steal == tdq || steal->tdq_transferable == 0)
                                   continue;
                           TDQ_LOCK(steal);
                           goto steal;
                   }
                   TDQ_UNLOCK(tdq);
           }
           /*
            * Find the least loaded CPU with a transferable thread and attempt
            * to steal it.  We make a lockless pass and then verify that the
            * thread is still available after locking.
            */
           for (;;) {
                   highcpu = 0;
                   highload = 0;
                   for (cpu = 0; cpu <= mp_maxid; cpu++) {
                           if (CPU_ABSENT(cpu))
                                   continue;
                           steal = TDQ_CPU(cpu);
                           if (steal->tdq_transferable == 0)
                                   continue;
                           if (steal->tdq_load < highload)
                                   continue;
                           highload = steal->tdq_load;
                           highcpu = cpu;
                   }
                   if (highload < steal_thresh)
                           break;
                   steal = TDQ_CPU(highcpu);
                   if (steal == tdq)
                           break;
                   tdq_lock_pair(tdq, steal);
                   if (steal->tdq_load >= steal_thresh && steal->tdq_transferable)
                           goto steal;
                   tdq_unlock_pair(tdq, steal);
           }
           spinlock_exit();
           return (1);
   steal:
           spinlock_exit();
           tdq_move(steal, tdq);
           TDQ_UNLOCK(steal);
           mi_switch(SW_VOL, NULL);
           thread_unlock(curthread);
   
           return (0);
   }
   
   /*
    * Notify a remote cpu of new work.  Sends an IPI if criteria are met.
    */
   static void
   tdq_notify(struct td_sched *ts)
   {
           struct thread *ctd;
           struct pcpu *pcpu;
           int cpri;
           int pri;
           int cpu;
   
           cpu = ts->ts_cpu;
           pri = ts->ts_thread->td_priority;
           pcpu = pcpu_find(cpu);
           ctd = pcpu->pc_curthread;
           cpri = ctd->td_priority;
   
           /*
            * If our priority is not better than the current priority there is
            * nothing to do.
            */
           if (pri > cpri)
                   return;
           /*
            * Always IPI idle.
            */
           if (cpri > PRI_MIN_IDLE)
                   goto sendipi;
           /*
            * If we're realtime or better and there is timeshare or worse running
            * send an IPI.
            */
           if (pri < PRI_MAX_REALTIME && cpri > PRI_MAX_REALTIME)
                   goto sendipi;
           /*
            * Otherwise only IPI if we exceed the threshold.
            */
           if (pri > preempt_thresh)
                   return;
   sendipi:
           ipi_selected(1 << cpu, IPI_PREEMPT);
   }
   
   /*
    * Steals load from a timeshare queue.  Honors the rotating queue head
    * index.
    */
   static struct td_sched *
   runq_steal_from(struct runq *rq, int cpu, u_char start)
   {
           struct td_sched *ts;
           struct rqbits *rqb;
           struct rqhead *rqh;
           int first;
           int bit;
           int pri;
           int i;
   
           rqb = &rq->rq_status;
           bit = start & (RQB_BPW -1);
           pri = 0;
           first = 0;
   again:
           for (i = RQB_WORD(start); i < RQB_LEN; bit = 0, i++) {
                   if (rqb->rqb_bits[i] == 0)
                           continue;
                   if (bit != 0) {
                           for (pri = bit; pri < RQB_BPW; pri++)
                                   if (rqb->rqb_bits[i] & (1ul << pri))
                                           break;
                           if (pri >= RQB_BPW)
                                   continue;
                   } else
                           pri = RQB_FFS(rqb->rqb_bits[i]);
                   pri += (i << RQB_L2BPW);
                   rqh = &rq->rq_queues[pri];
                   TAILQ_FOREACH(ts, rqh, ts_procq) {
                           if (first && THREAD_CAN_MIGRATE(ts->ts_thread) &&
                               THREAD_CAN_SCHED(ts->ts_thread, cpu))
                                   return (ts);
                           first = 1;
                   }
           }
           if (start != 0) {
                   start = 0;
                   goto again;
           }
   
           return (NULL);
   }
   
   /*
    * Steals load from a standard linear queue.
    */
   static struct td_sched *
   runq_steal(struct runq *rq, int cpu)
   {
           struct rqhead *rqh;
           struct rqbits *rqb;
           struct td_sched *ts;
           int word;
           int bit;
   
           rqb = &rq->rq_status;
           for (word = 0; word < RQB_LEN; word++) {
                   if (rqb->rqb_bits[word] == 0)
                           continue;
                   for (bit = 0; bit < RQB_BPW; bit++) {
                           if ((rqb->rqb_bits[word] & (1ul << bit)) == 0)
                                   continue;
                           rqh = &rq->rq_queues[bit + (word << RQB_L2BPW)];
                           TAILQ_FOREACH(ts, rqh, ts_procq)
                                   if (THREAD_CAN_MIGRATE(ts->ts_thread) &&
                                       THREAD_CAN_SCHED(ts->ts_thread, cpu))
                                           return (ts);
                   }
           }
           return (NULL);
   }
   
   /*
    * Attempt to steal a thread in priority order from a thread queue.
    */
   static struct td_sched *
   tdq_steal(struct tdq *tdq, int cpu)
   {
           struct td_sched *ts;
   
           TDQ_LOCK_ASSERT(tdq, MA_OWNED);
           if ((ts = runq_steal(&tdq->tdq_realtime, cpu)) != NULL)
                   return (ts);
           if ((ts = runq_steal_from(&tdq->tdq_timeshare,
               cpu, tdq->tdq_ridx)) != NULL)
                   return (ts);
           return (runq_steal(&tdq->tdq_idle, cpu));
   }
   
   /*
    * Sets the thread lock and ts_cpu to match the requested cpu.  Unlocks the
    * current lock and returns with the assigned queue locked.
    */
   static inline struct tdq *
   sched_setcpu(struct td_sched *ts, int cpu, int flags)
   {
           struct thread *td;
           struct tdq *tdq;
   
           THREAD_LOCK_ASSERT(ts->ts_thread, MA_OWNED);
   
           tdq = TDQ_CPU(cpu);
           td = ts->ts_thread;
           ts->ts_cpu = cpu;
   
           /* If the lock matches just return the queue. */
           if (td->td_lock == TDQ_LOCKPTR(tdq))
                   return (tdq);
   #ifdef notyet
           /*
            * If the thread isn't running its lockptr is a
            * turnstile or a sleepqueue.  We can just lock_set without
            * blocking.
            */
           if (TD_CAN_RUN(td)) {
                   TDQ_LOCK(tdq);
                   thread_lock_set(td, TDQ_LOCKPTR(tdq));
                   return (tdq);
           }
   #endif
           /*
            * The hard case, migration, we need to block the thread first to
            * prevent order reversals with other cpus locks.
            */
           spinlock_enter();
           thread_lock_block(td);
           TDQ_LOCK(tdq);
           thread_lock_unblock(td, TDQ_LOCKPTR(tdq));
           spinlock_exit();
           return (tdq);
   }
   
   /*
   * Find the thread queue running the lowest priority thread.
   */
  static int
  tdq_lowestpri(struct thread *td)
  {
          struct tdq *tdq;
          int lowpri;
          int lowcpu;
          int lowload;
          int load;
          int cpu;
          int pri;
  
          lowload = 0;
          lowpri = lowcpu = 0;
          for (cpu = 0; cpu <= mp_maxid; cpu++) {
                  if (CPU_ABSENT(cpu))
                          continue;
                  if (!THREAD_CAN_SCHED(td, cpu))
                          continue;
                  tdq = TDQ_CPU(cpu);
                  pri = tdq->tdq_lowpri;
                  load = TDQ_CPU(cpu)->tdq_load;
                  CTR4(KTR_ULE,
                      "cpu %d pri %d lowcpu %d lowpri %d",
                      cpu, pri, lowcpu, lowpri);
                  if (pri < lowpri)
                          continue;
                  if (lowpri && lowpri == pri && load > lowload)
                          continue;
                  lowpri = pri;
                  lowcpu = cpu;
                  lowload = load;
          }
  
          return (lowcpu);
  }
  
  /*
   * Find the thread queue with the least load.
   */
  static int
  tdq_lowestload(struct thread *td)
  {
          struct tdq *tdq;
          int lowload;
          int lowpri;
          int lowcpu;
          int load;
          int cpu;
          int pri;
  
          lowcpu = 0;
          lowload = TDQ_CPU(0)->tdq_load;
          lowpri = TDQ_CPU(0)->tdq_lowpri;
          for (cpu = 1; cpu <= mp_maxid; cpu++) {
                  if (CPU_ABSENT(cpu))
                          continue;
                  if (!THREAD_CAN_SCHED(td, cpu))
                          continue;
                  tdq = TDQ_CPU(cpu);
                  load = tdq->tdq_load;
                  pri = tdq->tdq_lowpri;
                  CTR4(KTR_ULE, "cpu %d load %d lowcpu %d lowload %d",
                      cpu, load, lowcpu, lowload);
                  if (load > lowload)
                          continue;
                  if (load == lowload && pri < lowpri)
                          continue;
                  lowcpu = cpu;
                  lowload = load;
                  lowpri = pri;
          }
  
          return (lowcpu);
  }
  
  /*
   * Pick the destination cpu for sched_add().  Respects affinity and makes
   * a determination based on load or priority of available processors.
   */
  static int
  sched_pickcpu(struct thread *td, int flags)
  {
          struct tdq *tdq;
          struct td_sched *ts;
          cpumask_t mask;
          int self;
          int pri;
          int cpu;
  
          self = PCPU_GET(cpuid);
          ts = td->td_sched;
          if (smp_started == 0)
                  return (self);
          /*
           * Don't migrate a running thread from sched_switch().
           */
          if (flags & SRQ_OURSELF) {
                  CTR1(KTR_ULE, "YIELDING %d",
                      curthread->td_priority);
                  return (self);
          }
          pri = ts->ts_thread->td_priority;
          cpu = ts->ts_cpu;
          if (THREAD_CAN_SCHED(td, cpu)) {
                  /*
                   * Regardless of affinity, if the last cpu is idle
                   * send it there.
                   */
                  tdq = TDQ_CPU(cpu);
                  if (tdq->tdq_lowpri > PRI_MIN_IDLE) {
                          CTR5(KTR_ULE,
                      "ts_cpu %d idle, ltick %d ticks %d pri %d curthread %d",
                              ts->ts_cpu, ts->ts_rltick, ticks, pri,
                              tdq->tdq_lowpri);
                          return (ts->ts_cpu);
                  }
                  /*
                   * If we have affinity, try to place it on the cpu we
                   * last ran on.
                   */
                  if (SCHED_AFFINITY(ts) && tdq->tdq_lowpri > pri) {
                          CTR5(KTR_ULE,
                      "affinity for %d, ltick %d ticks %d pri %d curthread %d",
                              ts->ts_cpu, ts->ts_rltick, ticks, pri,
                              tdq->tdq_lowpri);
                          return (ts->ts_cpu);
                  }
          }
  
          /*
           * Look for an idle group.
           */
          CTR1(KTR_ULE, "tdq_idle %X", tdq_idle);
          mask = tdq_idle;
          while ((cpu = ffs(mask)) != 0) {
                  --cpu;
                  if (THREAD_CAN_SCHED(td, cpu))
                          return (cpu);
                  mask &= ~(1 << cpu);
          }
          /*
           * If there are no idle cores see if we can run the thread locally.
           * This may improve locality among sleepers and wakers when there
           * is shared data.
           */
          if (tryself && THREAD_CAN_SCHED(td, self) &&
              pri < curthread->td_priority) {
                  CTR1(KTR_ULE, "tryself %d",
                      curthread->td_priority);
                  return (self);
          }
          /*
           * Now search for the cpu running the lowest priority thread with
           * the least load.
           */
          if (pick_pri)
                  cpu = tdq_lowestpri(td);
          else
                  cpu = tdq_lowestload(td);
          return (cpu);
  }
  
  #endif  /* SMP */
  
  /*
   * Pick the highest priority task we have and return it.
   */
  static struct td_sched *
  tdq_choose(struct tdq *tdq)
  {
          struct td_sched *ts;
  
          TDQ_LOCK_ASSERT(tdq, MA_OWNED);
          ts = runq_choose(&tdq->tdq_realtime);
          if (ts != NULL)
                  return (ts);
          ts = runq_choose_from(&tdq->tdq_timeshare, tdq->tdq_ridx);
          if (ts != NULL) {
                  KASSERT(ts->ts_thread->td_priority >= PRI_MIN_TIMESHARE,
                      ("tdq_choose: Invalid priority on timeshare queue %d",
                      ts->ts_thread->td_priority));
                  return (ts);
          }
  
          ts = runq_choose(&tdq->tdq_idle);
          if (ts != NULL) {
                  KASSERT(ts->ts_thread->td_priority >= PRI_MIN_IDLE,
                      ("tdq_choose: Invalid priority on idle queue %d",
                      ts->ts_thread->td_priority));
                  return (ts);
          }
  
          return (NULL);
  }
  
  /*
   * Initialize a thread queue.
   */
  static void
  tdq_setup(struct tdq *tdq)
  {
  
          if (bootverbose)
                  printf("ULE: setup cpu %d\n", TDQ_ID(tdq));
          runq_init(&tdq->tdq_realtime);
          runq_init(&tdq->tdq_timeshare);
          runq_init(&tdq->tdq_idle);
          tdq->tdq_load = 0;
  }
  
  #ifdef SMP
  static void
  tdg_setup(struct tdq_group *tdg)
  {
          if (bootverbose)
                  printf("ULE: setup cpu group %d\n", TDG_ID(tdg));
          snprintf(tdg->tdg_name, sizeof(tdg->tdg_name),
              "sched lock %d", (int)TDG_ID(tdg));
          mtx_init(&tdg->tdg_lock, tdg->tdg_name, "sched lock",
              MTX_SPIN | MTX_RECURSE);
          LIST_INIT(&tdg->tdg_members);
          tdg->tdg_load = 0;
          tdg->tdg_transferable = 0;
          tdg->tdg_cpus = 0;
          tdg->tdg_mask = 0;
          tdg->tdg_cpumask = 0;
          tdg->tdg_idlemask = 0;
  }
  
  static void
  tdg_add(struct tdq_group *tdg, struct tdq *tdq)
  {
          if (tdg->tdg_mask == 0)
                  tdg->tdg_mask |= 1 << TDQ_ID(tdq);
          tdg->tdg_cpumask |= 1 << TDQ_ID(tdq);
          tdg->tdg_cpus++;
          tdq->tdq_group = tdg;
          tdq->tdq_lock = &tdg->tdg_lock;
          LIST_INSERT_HEAD(&tdg->tdg_members, tdq, tdq_siblings);
          if (bootverbose)
                  printf("ULE: adding cpu %d to group %d: cpus %d mask 0x%X\n",
                      TDQ_ID(tdq), TDG_ID(tdg), tdg->tdg_cpus, tdg->tdg_cpumask);
  }
  
  static void
  sched_setup_topology(void)
  {
          struct tdq_group *tdg;
          struct cpu_group *cg;
          int balance_groups;
          struct tdq *tdq;
          int i;
          int j;
  
          topology = 1;
          balance_groups = 0;
          for (i = 0; i < smp_topology->ct_count; i++) {
                  cg = &smp_topology->ct_group[i];
                  tdg = &tdq_groups[i];
                  /*
                   * Initialize the group.
                   */
                  tdg_setup(tdg);
                  /*
                   * Find all of the group members and add them.
                   */
                  for (j = 0; j < MAXCPU; j++) { 
                          if ((cg->cg_mask & (1 << j)) != 0) {
                                  tdq = TDQ_CPU(j);
                                  tdq_setup(tdq);
                                  tdg_add(tdg, tdq);
                          }
                  }
                  if (tdg->tdg_cpus > 1)
                          balance_groups = 1;
          }
          tdg_maxid = smp_topology->ct_count - 1;
          if (balance_groups)
                  sched_balance_groups();
  }
  
  static void
  sched_setup_smp(void)
  {
          struct tdq_group *tdg;
          struct tdq *tdq;
          int cpus;
          int i;
  
          for (cpus = 0, i = 0; i < MAXCPU; i++) {
                  if (CPU_ABSENT(i))
                          continue;
                  tdq = &tdq_cpu[i];
                  tdg = &tdq_groups[i];
                  /*
                   * Setup a tdq group with one member.
                   */
                  tdg_setup(tdg);
                  tdq_setup(tdq);
                  tdg_add(tdg, tdq);
                  cpus++;
          }
          tdg_maxid = cpus - 1;
  }
  
  /*
   * Fake a topology with one group containing all CPUs.
   */
  static void
  sched_fake_topo(void)
  {
  #ifdef SCHED_FAKE_TOPOLOGY
          static struct cpu_top top;
          static struct cpu_group group;
  
          top.ct_count = 1;
          top.ct_group = &group;
          group.cg_mask = all_cpus;
          group.cg_count = mp_ncpus;
          group.cg_children = 0;
          smp_topology = &top;
  #endif
  }
  #endif
  
  /*
   * Setup the thread queues and initialize the topology based on MD
   * information.
   */
  static void
  sched_setup(void *dummy)
  {
          struct tdq *tdq;
  
          tdq = TDQ_SELF();
  #ifdef SMP
          sched_fake_topo();
          /*
           * Setup tdqs based on a topology configuration or vanilla SMP based
           * on mp_maxid.
           */
          if (smp_topology == NULL)
                  sched_setup_smp();
          else 
                  sched_setup_topology();
          balance_tdq = tdq;
          sched_balance();
  #else
          tdq_setup(tdq);
          mtx_init(&tdq_lock, "sched lock", "sched lock", MTX_SPIN | MTX_RECURSE);
          tdq->tdq_lock = &tdq_lock;
  #endif
          /*
           * To avoid divide-by-zero, we set realstathz a dummy value
           * in case which sched_clock() called before sched_initticks().
           */
          realstathz = hz;
          sched_slice = (realstathz/10);  /* ~100ms */
          tickincr = 1 << SCHED_TICK_SHIFT;
  
          /* Add thread0's load since it's running. */
          TDQ_LOCK(tdq);
          thread0.td_lock = TDQ_LOCKPTR(TDQ_SELF());
          tdq_load_add(tdq, &td_sched0);
          TDQ_UNLOCK(tdq);
  }
  
  /*
   * This routine determines the tickincr after stathz and hz are setup.
   */
  /* ARGSUSED */
  static void
  sched_initticks(void *dummy)
  {
          int incr;
  
          realstathz = stathz ? stathz : hz;
          sched_slice = (realstathz/10);  /* ~100ms */
  
          /*
           * tickincr is shifted out by 10 to avoid rounding errors due to
           * hz not being evenly divisible by stathz on all platforms.
           */
          incr = (hz << SCHED_TICK_SHIFT) / realstathz;
          /*
           * This does not work for values of stathz that are more than
           * 1 << SCHED_TICK_SHIFT * hz.  In practice this does not happen.
           */
          if (incr == 0)
                  incr = 1;
          tickincr = incr;
  #ifdef SMP
          /*
           * Set the default balance interval now that we know
           * what realstathz is.
           */
          balance_interval = realstathz;
          /*
           * Set steal thresh to roughly log2(mp_ncpu) but no greater than 4. 
           * This prevents excess thrashing on large machines and excess idle 
           * on smaller machines.
           */
          steal_thresh = min(fls(mp_ncpus) - 1, 3);
          affinity = SCHED_AFFINITY_DEFAULT;
  #endif
  }
  
  
  /*
   * This is the core of the interactivity algorithm.  Determines a score based
   * on past behavior.  It is the ratio of sleep time to run time scaled to
   * a [0, 100] integer.  This is the voluntary sleep time of a process, which
   * differs from the cpu usage because it does not account for time spent
   * waiting on a run-queue.  Would be prettier if we had floating point.
   */
  static int
  sched_interact_score(struct thread *td)
  {
          struct td_sched *ts;
          int div;
  
          ts = td->td_sched;
          /*
           * The score is only needed if this is likely to be an interactive
           * task.  Don't go through the expense of computing it if there's
           * no chance.
           */
          if (sched_interact <= SCHED_INTERACT_HALF &&
                  ts->ts_runtime >= ts->ts_slptime)
                          return (SCHED_INTERACT_HALF);
  
          if (ts->ts_runtime > ts->ts_slptime) {
                  div = max(1, ts->ts_runtime / SCHED_INTERACT_HALF);
                  return (SCHED_INTERACT_HALF +
                      (SCHED_INTERACT_HALF - (ts->ts_slptime / div)));
          }
          if (ts->ts_slptime > ts->ts_runtime) {
                  div = max(1, ts->ts_slptime / SCHED_INTERACT_HALF);
                  return (ts->ts_runtime / div);
          }
          /* runtime == slptime */
          if (ts->ts_runtime)
                  return (SCHED_INTERACT_HALF);
  
          /*
           * This can happen if slptime and runtime are 0.
           */
          return (0);
  
  }
  
  /*
   * Scale the scheduling priority according to the "interactivity" of this
   * process.
   */
  static void
  sched_priority(struct thread *td)
  {
          int score;
          int pri;
  
          if (td->td_pri_class != PRI_TIMESHARE)
                  return;
          /*
           * If the score is interactive we place the thread in the realtime
           * queue with a priority that is less than kernel and interrupt
           * priorities.  These threads are not subject to nice restrictions.
           *
           * Scores greater than this are placed on the normal timeshare queue
           * where the priority is partially decided by the most recent cpu
           * utilization and the rest is decided by nice value.
           *
           * The nice value of the process has a linear effect on the calculated
           * score.  Negative nice values make it easier for a thread to be
           * considered interactive.
           */
          score = imax(0, sched_interact_score(td) + td->td_proc->p_nice);
          if (score < sched_interact) {
                  pri = PRI_MIN_REALTIME;
                  pri += ((PRI_MAX_REALTIME - PRI_MIN_REALTIME) / sched_interact)
                      * score;
                  KASSERT(pri >= PRI_MIN_REALTIME && pri <= PRI_MAX_REALTIME,
                      ("sched_priority: invalid interactive priority %d score %d",
                      pri, score));
          } else {
                  pri = SCHED_PRI_MIN;
                  if (td->td_sched->ts_ticks)
                          pri += SCHED_PRI_TICKS(td->td_sched);
                  pri += SCHED_PRI_NICE(td->td_proc->p_nice);
                  KASSERT(pri >= PRI_MIN_TIMESHARE && pri <= PRI_MAX_TIMESHARE,
                      ("sched_priority: invalid priority %d: nice %d, " 
                      "ticks %d ftick %d ltick %d tick pri %d",
                      pri, td->td_proc->p_nice, td->td_sched->ts_ticks,
                      td->td_sched->ts_ftick, td->td_sched->ts_ltick,
                      SCHED_PRI_TICKS(td->td_sched)));
          }
          sched_user_prio(td, pri);
  
          return;
  }
  
  /*
   * This routine enforces a maximum limit on the amount of scheduling history
   * kept.  It is called after either the slptime or runtime is adjusted.  This
   * function is ugly due to integer math.
   */
  static void
  sched_interact_update(struct thread *td)
  {
          struct td_sched *ts;
          u_int sum;
  
          ts = td->td_sched;
          sum = ts->ts_runtime + ts->ts_slptime;
          if (sum < SCHED_SLP_RUN_MAX)
                  return;
          /*
           * This only happens from two places:
           * 1) We have added an unusual amount of run time from fork_exit.
           * 2) We have added an unusual amount of sleep time from sched_sleep().
           */
          if (sum > SCHED_SLP_RUN_MAX * 2) {
                  if (ts->ts_runtime > ts->ts_slptime) {
                          ts->ts_runtime = SCHED_SLP_RUN_MAX;
                          ts->ts_slptime = 1;
                  } else {
                          ts->ts_slptime = SCHED_SLP_RUN_MAX;
                          ts->ts_runtime = 1;
                  }
                  return;
          }
          /*
           * If we have exceeded by more than 1/5th then the algorithm below
           * will not bring us back into range.  Dividing by two here forces
           * us into the range of [4/5 * SCHED_INTERACT_MAX, SCHED_INTERACT_MAX]
           */
          if (sum > (SCHED_SLP_RUN_MAX / 5) * 6) {
                  ts->ts_runtime /= 2;
                  ts->ts_slptime /= 2;
                  return;
          }
          ts->ts_runtime = (ts->ts_runtime / 5) * 4;
          ts->ts_slptime = (ts->ts_slptime / 5) * 4;
  }
  
  /*
   * Scale back the interactivity history when a child thread is created.  The
   * history is inherited from the parent but the thread may behave totally
   * differently.  For example, a shell spawning a compiler process.  We want
   * to learn that the compiler is behaving badly very quickly.
   */
  static void
  sched_interact_fork(struct thread *td)
  {
          int ratio;
          int sum;
  
          sum = td->td_sched->ts_runtime + td->td_sched->ts_slptime;
          if (sum > SCHED_SLP_RUN_FORK) {
                  ratio = sum / SCHED_SLP_RUN_FORK;
                  td->td_sched->ts_runtime /= ratio;
                  td->td_sched->ts_slptime /= ratio;
          }
  }
  
  /*
   * Called from proc0_init() to setup the scheduler fields.
   */
  void
  schedinit(void)
  {
  
          /*
           * Set up the scheduler specific parts of proc0.
           */
          proc0.p_sched = NULL; /* XXX */
          thread0.td_sched = &td_sched0;
          td_sched0.ts_ltick = ticks;
          td_sched0.ts_ftick = ticks;
          td_sched0.ts_thread = &thread0;
  }
  
  /*
   * This is only somewhat accurate since given many processes of the same
   * priority they will switch when their slices run out, which will be
   * at most sched_slice stathz ticks.
   */
  int
  sched_rr_interval(void)
  {
  
          /* Convert sched_slice to hz */
          return (hz/(realstathz/sched_slice));
  }
  
  /*
   * Update the percent cpu tracking information when it is requested or
   * the total history exceeds the maximum.  We keep a sliding history of
   * tick counts that slowly decays.  This is less precise than the 4BSD
   * mechanism since it happens with less regular and frequent events.
   */
  static void
  sched_pctcpu_update(struct td_sched *ts)
  {
  
          if (ts->ts_ticks == 0)
                  return;
          if (ticks - (hz / 10) < ts->ts_ltick &&
              SCHED_TICK_TOTAL(ts) < SCHED_TICK_MAX)
                  return;
          /*
           * Adjust counters and watermark for pctcpu calc.
           */
          if (ts->ts_ltick > ticks - SCHED_TICK_TARG)
                  ts->ts_ticks = (ts->ts_ticks / (ticks - ts->ts_ftick)) *
                              SCHED_TICK_TARG;
          else
                  ts->ts_ticks = 0;
          ts->ts_ltick = ticks;
          ts->ts_ftick = ts->ts_ltick - SCHED_TICK_TARG;
  }
  
  /*
   * Adjust the priority of a thread.  Move it to the appropriate run-queue
   * if necessary.  This is the back-end for several priority related
   * functions.
   */
  static void
  sched_thread_priority(struct thread *td, u_char prio)
  {
          struct td_sched *ts;
  
          CTR6(KTR_SCHED, "sched_prio: %p(%s) prio %d newprio %d by %p(%s)",
              td, td->td_proc->p_comm, td->td_priority, prio, curthread,
              curthread->td_proc->p_comm);
          ts = td->td_sched;
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          if (td->td_priority == prio)
                  return;
  
          if (TD_ON_RUNQ(td) && prio < td->td_priority) {
                  /*
                   * If the priority has been elevated due to priority
                   * propagation, we may have to move ourselves to a new
                   * queue.  This could be optimized to not re-add in some
                   * cases.
                   */
                  sched_rem(td);
                  td->td_priority = prio;
                  sched_add(td, SRQ_BORROWING);
          } else {
  #ifdef SMP
                  struct tdq *tdq;
  
                  tdq = TDQ_CPU(ts->ts_cpu);
                  if (prio < tdq->tdq_lowpri)
                          tdq->tdq_lowpri = prio;
  #endif
                  td->td_priority = prio;
          }
  }
  
  /*
   * Update a thread's priority when it is lent another thread's
   * priority.
   */
  void
  sched_lend_prio(struct thread *td, u_char prio)
  {
  
          td->td_flags |= TDF_BORROWING;
          sched_thread_priority(td, prio);
  }
  
  /*
   * Restore a thread's priority when priority propagation is
   * over.  The prio argument is the minimum priority the thread
   * needs to have to satisfy other possible priority lending
   * requests.  If the thread's regular priority is less
   * important than prio, the thread will keep a priority boost
   * of prio.
   */
  void
  sched_unlend_prio(struct thread *td, u_char prio)
  {
          u_char base_pri;
  
          if (td->td_base_pri >= PRI_MIN_TIMESHARE &&
              td->td_base_pri <= PRI_MAX_TIMESHARE)
                  base_pri = td->td_user_pri;
          else
                  base_pri = td->td_base_pri;
          if (prio >= base_pri) {
                  td->td_flags &= ~TDF_BORROWING;
                  sched_thread_priority(td, base_pri);
          } else
                  sched_lend_prio(td, prio);
  }
  
  /*
   * Standard entry for setting the priority to an absolute value.
   */
  void
  sched_prio(struct thread *td, u_char prio)
  {
          u_char oldprio;
  
          /* First, update the base priority. */
          td->td_base_pri = prio;
  
          /*
           * If the thread is borrowing another thread's priority, don't
           * ever lower the priority.
           */
          if (td->td_flags & TDF_BORROWING && td->td_priority < prio)
                  return;
  
          /* Change the real priority. */
          oldprio = td->td_priority;
          sched_thread_priority(td, prio);
  
          /*
           * If the thread is on a turnstile, then let the turnstile update
           * its state.
           */
          if (TD_ON_LOCK(td) && oldprio != prio)
                  turnstile_adjust(td, oldprio);
  }
  
  /*
   * Set the base user priority, does not effect current running priority.
   */
  void
  sched_user_prio(struct thread *td, u_char prio)
  {
          u_char oldprio;
  
          td->td_base_user_pri = prio;
          if (td->td_flags & TDF_UBORROWING && td->td_user_pri <= prio)
                  return;
          oldprio = td->td_user_pri;
          td->td_user_pri = prio;
  }
  
  void
  sched_lend_user_prio(struct thread *td, u_char prio)
  {
          u_char oldprio;
  
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          td->td_flags |= TDF_UBORROWING;
          oldprio = td->td_user_pri;
          td->td_user_pri = prio;
  }
  
  void
  sched_unlend_user_prio(struct thread *td, u_char prio)
  {
          u_char base_pri;
  
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          base_pri = td->td_base_user_pri;
          if (prio >= base_pri) {
                  td->td_flags &= ~TDF_UBORROWING;
                  sched_user_prio(td, base_pri);
          } else {
                  sched_lend_user_prio(td, prio);
          }
  }
  
  /*
   * Add the thread passed as 'newtd' to the run queue before selecting
   * the next thread to run.  This is only used for KSE.
   */
  static void
  sched_switchin(struct tdq *tdq, struct thread *td)
  {
  #ifdef SMP
          spinlock_enter();
          TDQ_UNLOCK(tdq);
          thread_lock(td);
          spinlock_exit();
          sched_setcpu(td->td_sched, TDQ_ID(tdq), SRQ_YIELDING);
  #else
          td->td_lock = TDQ_LOCKPTR(tdq);
  #endif
          tdq_add(tdq, td, SRQ_YIELDING);
          MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
  }
  
  /*
   * Handle migration from sched_switch().  This happens only for
   * cpu binding.
   */
  static struct mtx *
  sched_switch_migrate(struct tdq *tdq, struct thread *td, int flags)
  {
          struct tdq *tdn;
  
          tdn = TDQ_CPU(td->td_sched->ts_cpu);
  #ifdef SMP
          /*
           * Do the lock dance required to avoid LOR.  We grab an extra
           * spinlock nesting to prevent preemption while we're
           * not holding either run-queue lock.
           */
          spinlock_enter();
          thread_lock_block(td);  /* This releases the lock on tdq. */
  
          /*
           * Acquire both run-queue locks before placing the thread on the new
           * run-queue to avoid deadlocks created by placing a thread with a
           * blocked lock on the run-queue of a remote processor.  The deadlock
           * occurs when a third processor attempts to lock the two queues in
           * question while the target processor is spinning with its own
           * run-queue lock held while waiting for the blocked lock to clear.
           */
          if (TDQ_LOCKPTR(tdn) == TDQ_LOCKPTR(tdq)) {
                  TDQ_LOCK(tdq);
                  tdq_add(tdn, td, flags);
                  tdq_notify(td->td_sched);
          } else {
                  tdq_lock_pair(tdn, tdq);
                  tdq_add(tdn, td, flags);
                  tdq_notify(td->td_sched);
                  TDQ_UNLOCK(tdn);
          }
          spinlock_exit();
  #endif
          return (TDQ_LOCKPTR(tdn));
  }
  
  /*
   * Variadic version of thread_lock_unblock() that does not assume td_lock
   * is blocked.
   */
  static inline void
  thread_unblock_switch(struct thread *td, struct mtx *mtx)
  {
          atomic_store_rel_ptr((volatile uintptr_t *)&td->td_lock,
              (uintptr_t)mtx);
  }
  
  /*
   * Switch threads.  This function has to handle threads coming in while
   * blocked for some reason, running, or idle.  It also must deal with
   * migrating a thread from one queue to another as running threads may
   * be assigned elsewhere via binding.
   */
  void
  sched_switch(struct thread *td, struct thread *newtd, int flags)
  {
          struct tdq *tdq;
          struct td_sched *ts;
          struct mtx *mtx;
          int srqflag;
          int cpuid;
  
          THREAD_LOCK_ASSERT(td, MA_OWNED);
  
          cpuid = PCPU_GET(cpuid);
          tdq = TDQ_CPU(cpuid);
          ts = td->td_sched;
          mtx = td->td_lock;
  #ifdef SMP
          ts->ts_rltick = ticks;
          if (newtd && newtd->td_priority < tdq->tdq_lowpri)
                  tdq->tdq_lowpri = newtd->td_priority;
  #endif
          td->td_lastcpu = td->td_oncpu;
          td->td_oncpu = NOCPU;
          td->td_flags &= ~TDF_NEEDRESCHED;
          td->td_owepreempt = 0;
          /*
           * The lock pointer in an idle thread should never change.  Reset it
           * to CAN_RUN as well.
           */
          if (TD_IS_IDLETHREAD(td)) {
                  MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
                  TD_SET_CAN_RUN(td);
          } else if (TD_IS_RUNNING(td)) {
                  MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
                  tdq_load_rem(tdq, ts);
                  srqflag = (flags & SW_PREEMPT) ?
                      SRQ_OURSELF|SRQ_YIELDING|SRQ_PREEMPTED :
                      SRQ_OURSELF|SRQ_YIELDING;
  #ifdef SMP
                  if (THREAD_CAN_MIGRATE(td) && !THREAD_CAN_SCHED(td, ts->ts_cpu))
                          ts->ts_cpu = sched_pickcpu(td, 0);
  #endif
                  if (ts->ts_cpu == cpuid)
                          tdq_add(tdq, td, srqflag);
                  else {
                          KASSERT(THREAD_CAN_MIGRATE(td) ||
                              (ts->ts_flags & TSF_BOUND) != 0,
                              ("Thread %p shouldn't migrate", td));
                          mtx = sched_switch_migrate(tdq, td, srqflag);
                  }
          } else {
                  /* This thread must be going to sleep. */
                  TDQ_LOCK(tdq);
                  mtx = thread_lock_block(td);
                  tdq_load_rem(tdq, ts);
          }
          /*
           * We enter here with the thread blocked and assigned to the
           * appropriate cpu run-queue or sleep-queue and with the current
           * thread-queue locked.
           */
          TDQ_LOCK_ASSERT(tdq, MA_OWNED | MA_NOTRECURSED);
          /*
           * If KSE assigned a new thread just add it here and let choosethread
           * select the best one.
           */
          if (newtd != NULL)
                  sched_switchin(tdq, newtd);
          newtd = choosethread();
          /*
           * Call the MD code to switch contexts if necessary.
           */
          if (td != newtd) {
  #ifdef  HWPMC_HOOKS
                  if (PMC_PROC_IS_USING_PMCS(td->td_proc))
                          PMC_SWITCH_CONTEXT(td, PMC_FN_CSW_OUT);
  #endif
                  TDQ_LOCKPTR(tdq)->mtx_lock = (uintptr_t)newtd;
  
  #ifdef KDTRACE_HOOKS
                  /*
                   * If DTrace has set the active vtime enum to anything
                   * other than INACTIVE (0), then it should have set the
                   * function to call.
                   */
                  if (dtrace_vtime_active)
                          (*dtrace_vtime_switch_func)(newtd);
  #endif
                  cpu_switch(td, newtd, mtx);
                  /*
                   * We may return from cpu_switch on a different cpu.  However,
                   * we always return with td_lock pointing to the current cpu's
                   * run queue lock.
                   */
                  cpuid = PCPU_GET(cpuid);
                  tdq = TDQ_CPU(cpuid);
  #ifdef  HWPMC_HOOKS
                  if (PMC_PROC_IS_USING_PMCS(td->td_proc))
                          PMC_SWITCH_CONTEXT(td, PMC_FN_CSW_IN);
  #endif
          } else
                  thread_unblock_switch(td, mtx);
          /*
           * Assert that all went well and return.
           */
  #ifdef SMP
          /* We should always get here with the lowest priority td possible */
          tdq->tdq_lowpri = td->td_priority;
  #endif
          TDQ_LOCK_ASSERT(tdq, MA_OWNED|MA_NOTRECURSED);
          MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
          td->td_oncpu = cpuid;
  }
  
  /*
   * Adjust thread priorities as a result of a nice request.
   */
  void
  sched_nice(struct proc *p, int nice)
  {
          struct thread *td;
  
          PROC_LOCK_ASSERT(p, MA_OWNED);
          PROC_SLOCK_ASSERT(p, MA_OWNED);
  
          p->p_nice = nice;
          FOREACH_THREAD_IN_PROC(p, td) {
                  thread_lock(td);
                  sched_priority(td);
                  sched_prio(td, td->td_base_user_pri);
                  thread_unlock(td);
          }
  }
  
  /*
   * Record the sleep time for the interactivity scorer.
   */
  void
  sched_sleep(struct thread *td)
  {
  
          THREAD_LOCK_ASSERT(td, MA_OWNED);
  
          td->td_slptick = ticks;
  }
  
  /*
   * Schedule a thread to resume execution and record how long it voluntarily
   * slept.  We also update the pctcpu, interactivity, and priority.
   */
  void
  sched_wakeup(struct thread *td)
  {
          struct td_sched *ts;
          int slptick;
  
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          ts = td->td_sched;
          /*
           * If we slept for more than a tick update our interactivity and
           * priority.
           */
          slptick = td->td_slptick;
          td->td_slptick = 0;
          if (slptick && slptick != ticks) {
                  u_int hzticks;
  
                  hzticks = (ticks - slptick) << SCHED_TICK_SHIFT;
                  ts->ts_slptime += hzticks;
                  sched_interact_update(td);
                  sched_pctcpu_update(ts);
                  sched_priority(td);
          }
          /* Reset the slice value after we sleep. */
          ts->ts_slice = sched_slice;
          sched_add(td, SRQ_BORING);
  }
  
  /*
   * Penalize the parent for creating a new child and initialize the child's
   * priority.
   */
  void
  sched_fork(struct thread *td, struct thread *child)
  {
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          sched_fork_thread(td, child);
          /*
           * Penalize the parent and child for forking.
           */
          sched_interact_fork(child);
          sched_priority(child);
          td->td_sched->ts_runtime += tickincr;
          sched_interact_update(td);
          sched_priority(td);
  }
  
  /*
   * Fork a new thread, may be within the same process.
   */
  void
  sched_fork_thread(struct thread *td, struct thread *child)
  {
          struct td_sched *ts;
          struct td_sched *ts2;
  
          /*
           * Initialize child.
           */
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          sched_newthread(child);
          child->td_lock = TDQ_LOCKPTR(TDQ_SELF());
          child->td_cpuset = cpuset_ref(td->td_cpuset);
          ts = td->td_sched;
          ts2 = child->td_sched;
          ts2->ts_cpu = ts->ts_cpu;
          ts2->ts_runq = NULL;
          /*
           * Grab our parents cpu estimation information and priority.
           */
          ts2->ts_ticks = ts->ts_ticks;
          ts2->ts_ltick = ts->ts_ltick;
          ts2->ts_incrtick = ts->ts_incrtick;
          ts2->ts_ftick = ts->ts_ftick;
          child->td_user_pri = td->td_user_pri;
          child->td_base_user_pri = td->td_base_user_pri;
          /*
           * And update interactivity score.
           */
          ts2->ts_slptime = ts->ts_slptime;
          ts2->ts_runtime = ts->ts_runtime;
          ts2->ts_slice = 1;      /* Attempt to quickly learn interactivity. */
  }
  
  /*
   * Adjust the priority class of a thread.
   */
  void
  sched_class(struct thread *td, int class)
  {
  
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          if (td->td_pri_class == class)
                  return;
  
  #ifdef SMP
          /*
           * On SMP if we're on the RUNQ we must adjust the transferable
           * count because could be changing to or from an interrupt
           * class.
           */
          if (TD_ON_RUNQ(td)) {
                  struct tdq *tdq;
  
                  tdq = TDQ_CPU(td->td_sched->ts_cpu);
                  if (THREAD_CAN_MIGRATE(td)) {
                          tdq->tdq_transferable--;
                          tdq->tdq_group->tdg_transferable--;
                  }
                  td->td_pri_class = class;
                  if (THREAD_CAN_MIGRATE(td)) {
                          tdq->tdq_transferable++;
                          tdq->tdq_group->tdg_transferable++;
                  }
          }
  #endif
          td->td_pri_class = class;
  }
  
  /*
   * Return some of the child's priority and interactivity to the parent.
   */
  void
  sched_exit(struct proc *p, struct thread *child)
  {
          struct thread *td;
          
          CTR3(KTR_SCHED, "sched_exit: %p(%s) prio %d",
              child, child->td_proc->p_comm, child->td_priority);
  
          PROC_SLOCK_ASSERT(p, MA_OWNED);
          td = FIRST_THREAD_IN_PROC(p);
          sched_exit_thread(td, child);
  }
  
  /*
   * Penalize another thread for the time spent on this one.  This helps to
   * worsen the priority and interactivity of processes which schedule batch
   * jobs such as make.  This has little effect on the make process itself but
   * causes new processes spawned by it to receive worse scores immediately.
   */
  void
  sched_exit_thread(struct thread *td, struct thread *child)
  {
  
          CTR3(KTR_SCHED, "sched_exit_thread: %p(%s) prio %d",
              child, child->td_proc->p_comm, child->td_priority);
  
  #ifdef KSE
          /*
           * KSE forks and exits so often that this penalty causes short-lived
           * threads to always be non-interactive.  This causes mozilla to
           * crawl under load.
           */
          if ((td->td_pflags & TDP_SA) && td->td_proc == child->td_proc)
                  return;
  #endif
          /*
           * Give the child's runtime to the parent without returning the
           * sleep time as a penalty to the parent.  This causes shells that
           * launch expensive things to mark their children as expensive.
           */
          thread_lock(td);
          td->td_sched->ts_runtime += child->td_sched->ts_runtime;
          sched_interact_update(td);
          sched_priority(td);
          thread_unlock(td);
  }
  
  /*
   * Fix priorities on return to user-space.  Priorities may be elevated due
   * to static priorities in msleep() or similar.
   */
  void
  sched_userret(struct thread *td)
  {
          /*
           * XXX we cheat slightly on the locking here to avoid locking in  
           * the usual case.  Setting td_priority here is essentially an
           * incomplete workaround for not setting it properly elsewhere.
           * Now that some interrupt handlers are threads, not setting it
           * properly elsewhere can clobber it in the window between setting
           * it here and returning to user mode, so don't waste time setting
           * it perfectly here.
           */
          KASSERT((td->td_flags & TDF_BORROWING) == 0,
              ("thread with borrowed priority returning to userland"));
          if (td->td_priority != td->td_user_pri) {
                  thread_lock(td);
                  td->td_priority = td->td_user_pri;
                  td->td_base_pri = td->td_user_pri;
                  thread_unlock(td);
          }
  }
  
  /*
   * Handle a stathz tick.  This is really only relevant for timeshare
   * threads.
   */
  void
  sched_clock(struct thread *td)
  {
          struct tdq *tdq;
          struct td_sched *ts;
  
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          tdq = TDQ_SELF();
  #ifdef SMP
          /*
           * We run the long term load balancer infrequently on the first cpu.
           */
          if (balance_tdq == tdq) {
                  if (balance_ticks && --balance_ticks == 0)
                          sched_balance();
                  if (balance_group_ticks && --balance_group_ticks == 0)
                          sched_balance_groups();
          }
  #endif
          /*
           * Advance the insert index once for each tick to ensure that all
           * threads get a chance to run.
           */
          if (tdq->tdq_idx == tdq->tdq_ridx) {
                  tdq->tdq_idx = (tdq->tdq_idx + 1) % RQ_NQS;
                  if (TAILQ_EMPTY(&tdq->tdq_timeshare.rq_queues[tdq->tdq_ridx]))
                          tdq->tdq_ridx = tdq->tdq_idx;
          }
          ts = td->td_sched;
          if (td->td_pri_class & PRI_FIFO_BIT)
                  return;
          if (td->td_pri_class == PRI_TIMESHARE) {
                  /*
                   * We used a tick; charge it to the thread so
                   * that we can compute our interactivity.
                   */
                  td->td_sched->ts_runtime += tickincr;
                  sched_interact_update(td);
          }
          /*
           * We used up one time slice.
           */
          if (--ts->ts_slice > 0)
                  return;
          /*
           * We're out of time, recompute priorities and requeue.
           */
          sched_priority(td);
          td->td_flags |= TDF_NEEDRESCHED;
  }
  
  /*
   * Called once per hz tick.  Used for cpu utilization information.  This
   * is easier than trying to scale based on stathz.
   */
  void
  sched_tick(void)
  {
          struct td_sched *ts;
  
          ts = curthread->td_sched;
          /*
           * Ticks is updated asynchronously on a single cpu.  Check here to
           * avoid incrementing ts_ticks multiple times in a single tick.
           */
          if (ts->ts_incrtick == ticks)
                  return;
          /* Adjust ticks for pctcpu */
          ts->ts_ticks += 1 << SCHED_TICK_SHIFT;
          ts->ts_incrtick = ticks;
          ts->ts_ltick = ticks;
          /*
           * Update if we've exceeded our desired tick threshhold by over one
           * second.
           */
          if (ts->ts_ftick + SCHED_TICK_MAX < ts->ts_ltick)
                  sched_pctcpu_update(ts);
  }
  
  /*
   * Return whether the current CPU has runnable tasks.  Used for in-kernel
   * cooperative idle threads.
   */
  int
  sched_runnable(void)
  {
          struct tdq *tdq;
          int load;
  
          load = 1;
  
          tdq = TDQ_SELF();
          if ((curthread->td_flags & TDF_IDLETD) != 0) {
                  if (tdq->tdq_load > 0)
                          goto out;
          } else
                  if (tdq->tdq_load - 1 > 0)
                          goto out;
          load = 0;
  out:
          return (load);
  }
  
  /*
   * Choose the highest priority thread to run.  The thread is removed from
   * the run-queue while running however the load remains.  For SMP we set
   * the tdq in the global idle bitmask if it idles here.
   */
  struct thread *
  sched_choose(void)
  {
  #ifdef SMP
          struct tdq_group *tdg;
  #endif
          struct td_sched *ts;
          struct tdq *tdq;
  
          tdq = TDQ_SELF();
          TDQ_LOCK_ASSERT(tdq, MA_OWNED);
          ts = tdq_choose(tdq);
          if (ts) {
                  tdq_runq_rem(tdq, ts);
                  return (ts->ts_thread);
          }
  #ifdef SMP
          /*
           * We only set the idled bit when all of the cpus in the group are
           * idle.  Otherwise we could get into a situation where a thread bounces
           * back and forth between two idle cores on seperate physical CPUs.
           */
          tdg = tdq->tdq_group;
          tdg->tdg_idlemask |= PCPU_GET(cpumask);
          if (tdg->tdg_idlemask == tdg->tdg_cpumask)
                  atomic_set_int(&tdq_idle, tdg->tdg_mask);
          tdq->tdq_lowpri = PRI_MAX_IDLE;
  #endif
          return (PCPU_GET(idlethread));
  }
  
  /*
   * Set owepreempt if necessary.  Preemption never happens directly in ULE,
   * we always request it once we exit a critical section.
   */
  static inline void
  sched_setpreempt(struct thread *td)
  {
          struct thread *ctd;
          int cpri;
          int pri;
  
          ctd = curthread;
          pri = td->td_priority;
          cpri = ctd->td_priority;
          if (td->td_priority < ctd->td_priority)
                  curthread->td_flags |= TDF_NEEDRESCHED;
          if (panicstr != NULL || pri >= cpri || cold || TD_IS_INHIBITED(ctd))
                  return;
          /*
           * Always preempt IDLE threads.  Otherwise only if the preempting
           * thread is an ithread.
           */
          if (pri > preempt_thresh && cpri < PRI_MIN_IDLE)
                  return;
          ctd->td_owepreempt = 1;
          return;
  }
  
  /*
   * Add a thread to a thread queue.  Initializes priority, slice, runq, and
   * add it to the appropriate queue.  This is the internal function called
   * when the tdq is predetermined.
   */
  void
  tdq_add(struct tdq *tdq, struct thread *td, int flags)
  {
          struct td_sched *ts;
          int class;
  #ifdef SMP
          int cpumask;
  #endif
  
          TDQ_LOCK_ASSERT(tdq, MA_OWNED);
          KASSERT((td->td_inhibitors == 0),
              ("sched_add: trying to run inhibited thread"));
          KASSERT((TD_CAN_RUN(td) || TD_IS_RUNNING(td)),
              ("sched_add: bad thread state"));
          KASSERT(td->td_flags & TDF_INMEM,
              ("sched_add: thread swapped out"));
  
          ts = td->td_sched;
          class = PRI_BASE(td->td_pri_class);
          TD_SET_RUNQ(td);
          if (ts->ts_slice == 0)
                  ts->ts_slice = sched_slice;
          /*
           * Pick the run queue based on priority.
           */
          if (td->td_priority <= PRI_MAX_REALTIME)
                  ts->ts_runq = &tdq->tdq_realtime;
          else if (td->td_priority <= PRI_MAX_TIMESHARE)
                  ts->ts_runq = &tdq->tdq_timeshare;
          else
                  ts->ts_runq = &tdq->tdq_idle;
  #ifdef SMP
          cpumask = 1 << ts->ts_cpu;
          /*
           * If we had been idle, clear our bit in the group and potentially
           * the global bitmap.
           */
          if ((class != PRI_IDLE && class != PRI_ITHD) &&
              (tdq->tdq_group->tdg_idlemask & cpumask) != 0) {
                  /*
                   * Check to see if our group is unidling, and if so, remove it
                   * from the global idle mask.
                   */
                  if (tdq->tdq_group->tdg_idlemask ==
                      tdq->tdq_group->tdg_cpumask)
                          atomic_clear_int(&tdq_idle, tdq->tdq_group->tdg_mask);
                  /*
                   * Now remove ourselves from the group specific idle mask.
                   */
                  tdq->tdq_group->tdg_idlemask &= ~cpumask;
          }
          if (td->td_priority < tdq->tdq_lowpri)
                  tdq->tdq_lowpri = td->td_priority;
  #endif
          tdq_runq_add(tdq, ts, flags);
          tdq_load_add(tdq, ts);
  }
  
  /*
   * Select the target thread queue and add a thread to it.  Request
   * preemption or IPI a remote processor if required.
   */
  void
  sched_add(struct thread *td, int flags)
  {
          struct td_sched *ts;
          struct tdq *tdq;
  #ifdef SMP
          int cpuid;
          int cpu;
  #endif
          CTR5(KTR_SCHED, "sched_add: %p(%s) prio %d by %p(%s)",
              td, td->td_proc->p_comm, td->td_priority, curthread,
              curthread->td_proc->p_comm);
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          ts = td->td_sched;
          /*
           * Recalculate the priority before we select the target cpu or
           * run-queue.
           */
          if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
                  sched_priority(td);
  #ifdef SMP
          cpuid = PCPU_GET(cpuid);
          /*
           * Pick the destination cpu and if it isn't ours transfer to the
           * target cpu.
           */
          if (td->td_priority <= PRI_MAX_ITHD && THREAD_CAN_MIGRATE(td) &&
              curthread->td_intr_nesting_level)
                  ts->ts_cpu = cpuid;
          if (!THREAD_CAN_MIGRATE(td))
                  cpu = ts->ts_cpu;
          else
                  cpu = sched_pickcpu(td, flags);
          tdq = sched_setcpu(ts, cpu, flags);
          tdq_add(tdq, td, flags);
          if (cpu != cpuid) {
                  tdq_notify(ts);
                  return;
          }
  #else
          tdq = TDQ_SELF();
          TDQ_LOCK(tdq);
          /*
           * Now that the thread is moving to the run-queue, set the lock
           * to the scheduler's lock.
           */
          thread_lock_set(td, TDQ_LOCKPTR(tdq));
          tdq_add(tdq, td, flags);
  #endif
          if (!(flags & SRQ_YIELDING))
                  sched_setpreempt(td);
  }
  
  /*
   * Remove a thread from a run-queue without running it.  This is used
   * when we're stealing a thread from a remote queue.  Otherwise all threads
   * exit by calling sched_exit_thread() and sched_throw() themselves.
   */
  void
  sched_rem(struct thread *td)
  {
          struct tdq *tdq;
          struct td_sched *ts;
  
          CTR5(KTR_SCHED, "sched_rem: %p(%s) prio %d by %p(%s)",
              td, td->td_proc->p_comm, td->td_priority, curthread,
              curthread->td_proc->p_comm);
          ts = td->td_sched;
          tdq = TDQ_CPU(ts->ts_cpu);
          TDQ_LOCK_ASSERT(tdq, MA_OWNED);
          MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
          KASSERT(TD_ON_RUNQ(td),
              ("sched_rem: thread not on run queue"));
          tdq_runq_rem(tdq, ts);
          tdq_load_rem(tdq, ts);
          TD_SET_CAN_RUN(td);
  }
  
  /*
   * Fetch cpu utilization information.  Updates on demand.
   */
  fixpt_t
  sched_pctcpu(struct thread *td)
  {
          fixpt_t pctcpu;
          struct td_sched *ts;
  
          pctcpu = 0;
          ts = td->td_sched;
          if (ts == NULL)
                  return (0);
  
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          if (ts->ts_ticks) {
                  int rtick;
  
                  sched_pctcpu_update(ts);
                  /* How many rtick per second ? */
                  rtick = min(SCHED_TICK_HZ(ts) / SCHED_TICK_SECS, hz);
                  pctcpu = (FSCALE * ((FSCALE * rtick)/hz)) >> FSHIFT;
          }
  
          return (pctcpu);
  }
  
  /*
   * Enforce affinity settings for a thread.  Called after adjustments to
   * cpumask.
   */
  void
  sched_affinity(struct thread *td)
  {
  #ifdef SMP
          struct td_sched *ts;
  
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          ts = td->td_sched;
          if (THREAD_CAN_SCHED(td, ts->ts_cpu))
                  return;
          if (TD_ON_RUNQ(td)) {
                  sched_rem(td);
                  sched_add(td, SRQ_BORING);
                  return;
          }
          if (!TD_IS_RUNNING(td))
                  return;
          /*
           * Force a switch before returning to userspace.  If the
           * target thread is not running locally send an ipi to force
           * the issue.
           */
          td->td_flags |= TDF_NEEDRESCHED;
          if (td != curthread)
                  ipi_selected(1 << ts->ts_cpu, IPI_PREEMPT);
  #endif
  }
  
  /*
   * Bind a thread to a target cpu.
   */
  void
  sched_bind(struct thread *td, int cpu)
  {
          struct td_sched *ts;
  
          THREAD_LOCK_ASSERT(td, MA_OWNED|MA_NOTRECURSED);
          KASSERT(td == curthread, ("sched_bind: can only bind curthread"));
          ts = td->td_sched;
          if (ts->ts_flags & TSF_BOUND)
                  sched_unbind(td);
          KASSERT(THREAD_CAN_MIGRATE(td), ("%p must be migratable", td));
          ts->ts_flags |= TSF_BOUND;
  #ifdef SMP
          sched_pin();
          if (PCPU_GET(cpuid) == cpu)
                  return;
          ts->ts_cpu = cpu;
          /* When we return from mi_switch we'll be on the correct cpu. */
          mi_switch(SW_VOL, NULL);
  #endif
  }
  
  /*
   * Release a bound thread.
   */
  void
  sched_unbind(struct thread *td)
  {
          struct td_sched *ts;
  
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          KASSERT(td == curthread, ("sched_unbind: can only bind curthread"));
          ts = td->td_sched;
          if ((ts->ts_flags & TSF_BOUND) == 0)
                  return;
          ts->ts_flags &= ~TSF_BOUND;
  #ifdef SMP
          sched_unpin();
  #endif
  }
  
  int
  sched_is_bound(struct thread *td)
  {
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          return (td->td_sched->ts_flags & TSF_BOUND);
  }
  
  /*
   * Basic yield call.
   */
  void
  sched_relinquish(struct thread *td)
  {
          thread_lock(td);
          SCHED_STAT_INC(switch_relinquish);
          mi_switch(SW_VOL, NULL);
          thread_unlock(td);
  }
  
  /*
   * Return the total system load.
   */
  int
  sched_load(void)
  {
  #ifdef SMP
          int total;
          int i;
  
          total = 0;
          for (i = 0; i <= tdg_maxid; i++)
                  total += TDQ_GROUP(i)->tdg_load;
          return (total);
  #else
          return (TDQ_SELF()->tdq_sysload);
  #endif
  }
  
  int
  sched_sizeof_proc(void)
  {
          return (sizeof(struct proc));
  }
  
  int
  sched_sizeof_thread(void)
  {
          return (sizeof(struct thread) + sizeof(struct td_sched));
  }
  
  /*
   * The actual idle process.
   */
  void
  sched_idletd(void *dummy)
  {
          struct thread *td;
          struct tdq *tdq;
  
          td = curthread;
          tdq = TDQ_SELF();
          mtx_assert(&Giant, MA_NOTOWNED);
          /* ULE relies on preemption for idle interruption. */
          for (;;) {
  #ifdef SMP
                  if (tdq_idled(tdq))
                          cpu_idle();
  #else
                  cpu_idle();
  #endif
          }
  }
  
  /*
   * A CPU is entering for the first time or a thread is exiting.
   */
  void
  sched_throw(struct thread *td)
  {
          struct thread *newtd;
          struct tdq *tdq;
  
          tdq = TDQ_SELF();
          if (td == NULL) {
                  /* Correct spinlock nesting and acquire the correct lock. */
                  TDQ_LOCK(tdq);
                  spinlock_exit();
          } else {
                  MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
                  tdq_load_rem(tdq, td->td_sched);
          }
          KASSERT(curthread->td_md.md_spinlock_count == 1, ("invalid count"));
          newtd = choosethread();
          TDQ_LOCKPTR(tdq)->mtx_lock = (uintptr_t)newtd;
          PCPU_SET(switchtime, cpu_ticks());
          PCPU_SET(switchticks, ticks);
          cpu_throw(td, newtd);           /* doesn't return */
  }
  
  /*
   * This is called from fork_exit().  Just acquire the correct locks and
   * let fork do the rest of the work.
   */
  void
  sched_fork_exit(struct thread *td)
  {
          struct td_sched *ts;
          struct tdq *tdq;
          int cpuid;
  
          /*
           * Finish setting up thread glue so that it begins execution in a
           * non-nested critical section with the scheduler lock held.
           */
          cpuid = PCPU_GET(cpuid);
          tdq = TDQ_CPU(cpuid);
          ts = td->td_sched;
          if (TD_IS_IDLETHREAD(td))
                  td->td_lock = TDQ_LOCKPTR(tdq);
          MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
          td->td_oncpu = cpuid;
          TDQ_LOCK_ASSERT(tdq, MA_OWNED | MA_NOTRECURSED);
  }
  
  static SYSCTL_NODE(_kern, OID_AUTO, sched, CTLFLAG_RW, 0,
      "Scheduler");
  SYSCTL_STRING(_kern_sched, OID_AUTO, name, CTLFLAG_RD, "ULE", 0,
      "Scheduler name");
  SYSCTL_INT(_kern_sched, OID_AUTO, slice, CTLFLAG_RW, &sched_slice, 0,
      "Slice size for timeshare threads");
  SYSCTL_INT(_kern_sched, OID_AUTO, interact, CTLFLAG_RW, &sched_interact, 0,
       "Interactivity score threshold");
  SYSCTL_INT(_kern_sched, OID_AUTO, preempt_thresh, CTLFLAG_RW, &preempt_thresh,
       0,"Min priority for preemption, lower priorities have greater precedence");
  #ifdef SMP
  SYSCTL_INT(_kern_sched, OID_AUTO, pick_pri, CTLFLAG_RW, &pick_pri, 0,
      "Pick the target cpu based on priority rather than load.");
  SYSCTL_INT(_kern_sched, OID_AUTO, affinity, CTLFLAG_RW, &affinity, 0,
      "Number of hz ticks to keep thread affinity for");
  SYSCTL_INT(_kern_sched, OID_AUTO, tryself, CTLFLAG_RW, &tryself, 0, "");
  SYSCTL_INT(_kern_sched, OID_AUTO, balance, CTLFLAG_RW, &rebalance, 0,
      "Enables the long-term load balancer");
  SYSCTL_INT(_kern_sched, OID_AUTO, balance_interval, CTLFLAG_RW,
      &balance_interval, 0,
      "Average frequency in stathz ticks to run the long-term balancer");
  SYSCTL_INT(_kern_sched, OID_AUTO, steal_htt, CTLFLAG_RW, &steal_htt, 0,
      "Steals work from another hyper-threaded core on idle");
  SYSCTL_INT(_kern_sched, OID_AUTO, steal_idle, CTLFLAG_RW, &steal_idle, 0,
      "Attempts to steal work from other cores before idling");
  SYSCTL_INT(_kern_sched, OID_AUTO, steal_thresh, CTLFLAG_RW, &steal_thresh, 0,
      "Minimum load on remote cpu before we'll steal");
  SYSCTL_INT(_kern_sched, OID_AUTO, topology, CTLFLAG_RD, &topology, 0,
      "True when a topology has been specified by the MD code.");
  #endif
  
  /* ps compat.  All cpu percentages from ULE are weighted. */
  static int ccpu = 0;
  SYSCTL_INT(_kern, OID_AUTO, ccpu, CTLFLAG_RD, &ccpu, 0, "");
  
  
  #define KERN_SWITCH_INCLUDE 1
  #include "kern/kern_switch.c"

Cache object: 98828a38be0c81a472e19b41705b2d74